A correlative study of the structure and function of horizontal cells and other processes of the outer plexiform layer (OPL) of the frog retina is proposed. Neuronal connectivity will be studied by light and electron microscopy of serial sections of variously prepared retinas and cells stained selectively by Golgi silver impregnation or the injection of horseradish peroxidase (HRP). Intracellular recording will be used to determine functional cell properties such as receptive field size and shape, spectral sensitivity and center-surround organization. Penetrated cells will be injected with HRP and studied by light and electron microscopy to determine number, tye and spatial distribution of receptor contacts as well as the general morphology of the stained processes. These data will be used to test several hypotheses concerning receptor interaction, horizontal cell feedback onto receptors, lateral interaction among horizontal cells center-surround organization of bipolar cells. Thus the thrust of the proposal is to determine the connectivity of neuronal processes in the OPL of the retina and relate these data to the function of the processes.